An air conditioning system for automobiles commonly includes a cooling device. A refrigerant during a cooling process is compressed by a compressor driven by engine power and flows in a condenser. The refrigerant is then heat exchanged by air blast of a cooling fan of a blower unit, sequentially passes through a receiver driver, an expansion valve, and an evaporator, and flows in a compressor again. The air ventilated by the cooling fan is heat exchanged with the refrigerant passing through the evaporator, and flows in the interior in a state of cool air, thereby cooling inside the automobiles. A heating device includes a coolant of engine passing through a heater core and returning to the engine during a heating process. Air ventilated by an air blast fan is heat exchanged with the coolant passing through the heater core, and flows in the interior in the state of warm air, thereby heating inside the automobiles.
That is, the main function of the air conditioning system for automobiles is to provide a pleasant environment for passengers under various weather or running conditions.
In the air conditioning system for automobiles, ventilated air moves along an air duct that is a transfer passage of air, and is ventilated into inside the automobiles through an air vent connected to one end of the air duct. The air duct for the air conditioning system for automobiles is commonly manufactured by blow molding a polyethylene resin.
However, a solid type of air duct manufactured by molding the polyethylene resin has high density, thus increasing weight of the automobiles.
Further, the solid type of air duct generates condensation of moisture due to an inferior insulation property and lowers cooling/heating efficiency of the automobiles, and a discharged amount of carbon dioxide is increased, thus reducing automobile mileage.
Thus, a non-woven fabric is attached to an external part of the solid type of air duct to improve the insulation property and to reduce noise, but there are problems due to the weight increase and a more complexed manufacturing process.
To solve these problems, ongoing studies have been undertaken for applying a foam that is expanded by a blowing agent and has a light weight and an excellent insulation property as an air duct.
However, the expandable foam air duct may not have desired hardness due to limitations in a resin which constitutes the foam, and thus it is difficult to manufacture an air duct having satisfactory mechanical properties and surface quality.
Accordingly, there is a demand for the development of a resin molded product for an air duct having an excellent surface quality while securing good insulation and mechanical properties.